1. Field of the Invention
The present invention relates to the fields of chemistry and medicine. More specifically, the present invention relates to compounds and procedures useful in the treatment of cancer, or in the treatment of fungal infections.
2. Description of the Related Art
It is thought that a single, universal cellular mechanism controls the regulation of the eukaryotic cell cycle process. See, e.g., Hartwell, L. H. et al., Science (1989), 246: 629-34. It is also known that when an abnormality arises in the control mechanism of the cell cycle, cancer or an immune disorder may occur. Accordingly, as is also known, antitumor agents and immune suppressors may be among the substances that regular the cell cycle. Thus, new eukaryotic cell cycle inhibitors are needed as antitumor and immune-enhancing compounds, and should be useful in the treatment of human cancer as chemotherapeutic, anti-tumor agents. See, e.g., Roberge, M. et al., Cancer Res. (1994), 54, 6115-21.
Recently, it has been reported that tryprostatins A and B (which are diketopiperazines consisting of proline and isoprenylated tryptophan residues), and five other structurally-related diketopiperazines, inhibited cell cycle progression in the M phase, see Cui, C. et al., J. Antibiotics (1996), 49, 527-33; Cui, C. et al. J. Antibiotics (1996), 49, 534-40, and that these compounds also affect the microtubule assembly, see Usui, T. et al.Biochem J. (1998) 333, 543-48; Kondon, M. et al. J. Antibiotics (1998) 51, 801-04. Furthermore, natural and synthetic compounds have been reported to inhibit mitosis, thus inhibit the eukaryotic cell cycle, by binding to the colchicine binding-site (CLC-site) on tubulin, which is a macromolecule that consists of two 50 kDa subunits (α- and β-tubulin) and is the major constituent of microtubules. See, e.g., Iwasaki, S., Med. Res. Rev. (1993) 13, 183-198; Hamel, E. Med. Res. Rev. (1996) 16, 207-31; Weisenberg, R. C. et al., Biochemistry (1969) 7, 4466-79. Microtubules are thought to be involved in several essential cell functions, such as axonal transport, cell motility and determination of cell morphology. Therefore, inhibitors of microtubule function may have broad biological activity, and be applicable to medicinal and agrochemical purposes. It is also possible that colchicine (CLC)-site ligands such as CLC, steganacin, see Kupchan, S. M. et al., J. Am. Chem. Soc. (1973) 95, 1335-36, podophyllotoxin, see Sackett, D. L., Pharmacol. Ther. (1993) 59, 163-228, and combretastatins, see Pettit, G. R. et al., J. Med. Chem. (1995) 38, 166-67, may prove to be valuable as eukaryotic cell cycle inhibitors and, thus, may be useful as chemotherapeutic agents.
Although diketopiperazine-type metabolites have been isolated from various fungi as mycotoxins, see Horak R. M. et al., J.C.S. Chem. Comm. (1981) 1265-67; Ali M. et al., Toxicology Letters, (1989) 48, 235-41, or as secondary metabolites, see Smedsgaard J. et al., J. Microbiol. Meth. (1996) 25, 5-17, little is known about the specific structure of the diketopiperazine-type metabolites and their antitumor activity, particularly in vivo. Furthermore, even though known antitumor substances isolated from microorganism metabolites (including anthracyclins and mitomycins that exhibit antitumor activity by binding to DNA) have been used as antitumor agents, see Microorganic Pharmaceutical Chemistry, revised 2nd edition, edited by Yoshio Ueno & Satoshi Ohmura, Nankohdo Publishing Co., (1986)), and even though anti-tumor substances having non-DNA binding operating mechanism have been isolated from microorganism metabolites, see Minoru Yoshida, M. Protein Nucleic Acid Enzymes (1993) 38, 1753; and Iwasaki, N., Chemistry and Living Organisms, (1994) 32, No. 3, 153, there is a particular need for new microorganism metabolite-derived compounds having animal cell-specific proliferation-inhibiting activity and high antitumor activity and selectivity. There is therefore a related need for substantially purified, and structurally and biologically characterized fungal diketopiperazine-type metabolites and fungal diketopiperazine-type metabolite-derivatives.